Hi Kirill,NCQ is actually measured, so it is reliable.Rotational can be wrong, but you can write to it (e.g. at machinestartup) to obtain better handling of your disks.I am also a fan of auto-tuning, and trying to achieve it in cfq, butit is kind of complex, since there are many factors, and some of themaren't modeled by cfq currently.An example is that, on cheap SSDs or flash cards, small writes are farslower than anything else (they can take up to 0.5s), while a readwill usually take less than 1ms. Currently, CFQ has no way to handlethis extreme situation, since it uses just one idle value (8ms) forall transitions.

Corrado

On 1/7/10, Kirill Afonshin <kirill_nnov@mail.ru> wrote:> I think we should not rely on NCQ/non-NCQ or blk_queue_nonrot() because it> may be incorrect:> try this:>> find /sys/ -name rotational 2>/dev/null> find /sys/ -name rotational 2>/dev/null|xargs cat>> all devices are reported as rotational for me including ram, loop and usb> flash drive. Physical block size and optimal io size has invalid values for> all my usb flash drives.>> I think it would be better to do a short performance test before mount. It> will provide all necessary information for io scheduler. We doesn't need> information about NCQ and rotational. We need to predict how much time> specific io operation will take in current context.>> PS: I'm not native speaker.>> Best regards,> Kirill Afonshin>